In recent years, there have been proposed and developed various valve timing control technologies in which an intake-valve timing is controlled to an intermediate phase between a maximum phase-retard position and a maximum phase-advance position when starting an internal combustion engine from cold so as to ensure a good startability during engine cold-start operation. To realize this, it is generally known that an angular phase (a phase angle) of a camshaft relative to a timing sprocket is locked or held at the previously-noted intermediate phase by means of a lock pin of a lock mechanism during non-control for a variable valve timing control (VTC) device employing a hydraulically-operated vane-rotor-type timing variator.
However, during the non-control, the vane rotor of the VTC device tends to be forced in a phase-retard direction relatively to the sprocket owing to alternating torque acting on the camshaft. For the reasons discussed above, when the engine has stopped under a particular state where the angular phase of the vane rotor relative to the sprocket is held or positioned at an angular position retarded from the intermediate phase (i.e., the intermediate lock position), it is difficult to shift the vane rotor to the intermediate lock position by virtue of alternating torque.
To avoid this, in a VTC device as disclosed in German Patent document DE 10 2008 011 916 A1, a guide mechanism having a guide pin as well as a lock mechanism having lock pins, is provided for guiding rotary motion of a vane rotor (fixedly connected to a camshaft) relative to a timing sprocket (adapted to rotate in synchronism with rotation of an engine crankshaft) toward an intermediate lock position. According to the guide mechanism disclosed in DE 10 2008 011 916 A1, the vane rotor can be guided toward the intermediate lock position by virtue of a fluttering motion of the guide pin in a guide recess, caused by positive and negative fluctuations in alternating torque acting on the camshaft.
However, in the case of the VTC device disclosed in DE 10 2008 011 916 A1, assume that the guide pin moves out of the associated guide recess with a time lag after the lock pins have moved out of engagement with respective lock holes. There is an increased tendency for the guide pin to be undesirably caught on the edge of the guide recess. In such a case, it is hard to achieve a desired VTC function. Thus, it would be desirable to provide a means by which it is possible to suppress or avoid the guide pin from being undesirably caught on the edge of the guide recess during an unlocking period of the lock mechanism.